The invention relates generally to optical information processing and, in particular, to an integrated electro-optical cross-bar apparatus for performing parallel optical logic and arithmetic operations.
There is a fundamental difference between optical circuits, in which the information carriers are photons, and electronic circuits, where the carriers are electrons. In the former case the carriers do not interact with each other, while in the latter they do. This means that in optical devices there exist interconnect possibilities that do not exist with electronic hardware, in particular, interconnected parallel architectures which permit digital arithmetic and logic operations to be performed in a completely parallel, single step process. After the inputs are switched on, the output appears in the time it takes a photon to transit the device. No faster computation time is possible.
Copending application Serial Number 019,761, filed Feb. 27, 1987 of Falk et al describes an optical cross-bar arithmetic/logic unit that performs the abovementioned single step process by employing residue arithmetic. Residue arithmetic does not have a "carry" operation; that is, each "bit" in the representation is independent of the other. In residue arithmetic, each "bit" in a representation of a number is the decimal value of the number modulo the prime number corresponding to that position, called the modulus.
The optical cross-bar arithmetic/logic unit disclosed in the abovementioned copending application utilizes crossed optical paths of light configured to define intersecting regions with each other corresponding to truth table or logic table inputs. The intensity of light at each intersecting region is detected to determine if two units of light intensity are present at each intersection, thereby indicating a particular logic state.
In order to maximize performance and reduce the size of the optical cross-bar arithmetic/logic unit, it is desirable that the waveguides and electronic detectors of an optical cross-bar arithmetic/logic unit be formed together in a single integrated electro-optic chip. Difficulties arise in the fabrication of an electro-optic chip, however, as the desirable material properties for fabricating electronic sources, detectors and transistors are directly opposite to the properties needed for quality waveguides.